Recently a great deal of interest has been expressed in television systems which provide an image aspect ratio (i.e., the ratio of the width to the height of the image) such as 2:1, 16:9 or 5:3 greater than the conventional aspect ratio of 4:3 of present day conventional television systems conforming to a conventional transmission standard such as NTSC. The greater aspect ratios are more in-line wth human visual perception than the conventional 4:3 television aspect ratio. Accordingly, present day motion picture films produce images with an aspect ratio of 5:3 or greater.
It is desirable that a new transmission system for providing a widescreen television signal for reproducing widescreen images in widescreen television receivers will also be compatible with the existing conventional transmission standard and existing conventional television receivers. This means that the widescreen television signal should be capable of being transmitted through a single channel of a conventional transmission system having a limited transmission bandwidth (e.g., 6 MHz for NTSC) and also that when the widescreen television signal is processed in a conventional aspect ratio receiver a conventional aspect ratio image should be produced without significant degradation or artifacts.
One "backward compatible" widescreen television transmission system is described in U.S. patent application Ser. No. 078,150, entitled "Compatible Widescreen Television System", filed in the U. S. Patent and Trademark Office on July 27, 1987 in the names of C. H. Strolle, T. R. Smith, B. J. Roeder and M. A. Isnardi, and issued as U.S. Pat. No. 4,816,899 on Mar. 28, 1989. This system utilizes a widescreen television camera that is capable of scanning a scene so as to generate a widescreen television signal corresponding to an image having a widescreen aspect ratio (e.g., 5:3) greater than the conventional aspect ratio (e.g., 4:3) available from a conventional camera. The widescreen television signal has an active line interval containing the widescreen image information which is the same as an active line interval of a conventional aspect ratio television signal employed in the conventional transmission system (e.g., approximately 52.5 microseconds for NTSC).
If an image were reproduced in a conventional television receiver from the widescreen television signal in the form generated by the widescreen camera, the image would be compressed in time so that objects would appear thinner in the horizontal direction than normal. The widescreen television signal in the form generated by a widescreen camera also has a bandwidth which is greater than that of a conventional aspect ratio television signal generated by a conventional camera and can therefore not be transmitted in a single channel of the conventional transmission system without loss of information necessary for faithful reproduction of a widescreen image in a widescreen television receiver.
To solve these problems, the widescreen television system described in the Strolle et al. patent application utilizes an encoder to process the widescreen television signal produced by the widescreen camera prior to transmission to produce a television signal which contains information necessary for faithful widescreen image reproduction and which is also compatible with the conventional NTSC transmission system. When the compatible widescreen television signal is received and processed by a widescreen television receiver, a widescreen image is produced. When received and processed by a conventional aspect ratio television receiver, a conventional aspect ratio image without significant degradation or artifacts is produced.
Basically, the encoder expands in time portions of the widescreen television signal corresponding to a center image portion between left and right side image portions of the widescreen image. This is done so that a compressed image is not produced in a conventional television receiver and so that the bandwidth is reduced for transmission to a widescreen television receiver through a single conventional transmission channel without loss of information. The encoder also compresses in time the portions of the widescreen television signal corresponding to the left and right side widescreen image portions into image overscan regions so as not to be visible in the image displayed by a conventional aspect ratio television receiver. The time compression of the side signal portions causes an increase in bandwidth. To accommodate the increase in bandwidth, the side signal portions are partitioned in frequency into low and high frequency components. The low frequency component of time-compressed side signal portions are combined with the time-expanded center signal portion to form a first component of the transmitted signal. The high frequency component of the time-compressed side signal portions are modulated on a subcarrier to form a second component of the transmitted signal.
An improved "backward compatible" widescreen television system, which also provides for enhanced or extended definition images with greater than conventional horizontal and vertical image detail, is described in U.S. patent application 139,340, entitled "Extended Definition Widescreen Television Signal Processing System", filed in the U.S. Patent and Trademark Office on Dec. 29, 1987 in the name of M. A. Isnardi, and wall allowed on May 16, 1989.
The widescreen enhanced definition system is intended to use a widescreen high definition television camera that scans a scene so as to produce a television signal corresponding to an image having: a widescreen aspect ratio (e.g., 5:3) greater than the conventional aspect ratio (e.g., 4:3) available from a conventional camera; a high definition horizontal resolution (e.g., between 600 and 800 lines) greater than the conventional horizontal resolution (e.g., between 400 and 600 lines) available from a conventional camera; and a high definition vertical resolution (e.g., 1050 lines per frame) greater than the conventional vertical resolution (e.g., 525 lines per frame) available from a conventional camera. The resulting widescreen high definition television signal has a much greater bandwidth than the conventional television signal produced by a conventional camera and is reduced in bandwidth by an encoder (as will be described below in detail in connection with a detailed description of embodiments of the present invention) to produce a television signal capable of being transmitted in a single conventional channel having a limited bandwidth. Briefly, the encoded signal includes four components. The first and second components are similar to the first and second components of the widescreen television system described in the Strolle et al. patent application. The third component contains high frequency horizontal image detail for use in a widescreen enhanced definition television receiver to produce an increase in horizontal resolution. The fouth component contains information for use in a widescreen enhanced definition television receiver to reconstruct vertical detail which may otherwise be lost due to encoding process.